BETA

Email Bounce Error Codes

Complete reference for SMTP bounce codes, NDR errors, and delivery failures

🔧 Related Tools

ANALYSIS TOOLS
🔒 Full Checker Complete email deliverability scan: SPF, DKIM, DMARC, MX, blacklists & more. 📨 SPF Check and visualise your SPF record including the full DNS lookup tree. 🔑 DKIM Scan all known DKIM selectors and validate key strength for your domain. 📧 Email Headers Analyse raw email headers to trace delivery path and authentication results. 📬 Bounce Decoder Decode NDR bounce messages and SMTP error codes to diagnose delivery failures. 🦁 BIMI Verify your BIMI logo record and VMC certificate status. 🔐 DNSSEC Validate the DNSSEC chain of trust: DS, DNSKEY, and RRSIG records. 🔒 MTA-STS Check your MTA-STS DNS record and TLS policy file for enforced encryption. 📋 TLS-RPT Validate your TLS-RPT reporting address for email transport encryption reports. 🌍 WHOIS Look up domain registration details via RDAP.
DIAGNOSTIC TOOLS
🚫 Blacklist / RBL Check IPs and domains against major email blacklists and RBLs. 🌐 DNS Propagation Check DNS record propagation across multiple global resolvers simultaneously.
BUILDER TOOLS
🛡️ DMARC Builder Build a DMARC TXT record with the right policy, RUA/RUF and subdomain options. 🛠 SPF Builder Generate a validated SPF record by selecting your email senders. ✂️ Route 53 Splitter Split long DKIM or SPF TXT records for AWS Route 53's 255-character limit.

Tier 1 — Very Common

🔴 550 5.1.1
Mailbox Does Not Exist
🔴 501 5.1.8
Bad Sender Address
🔴 550 5.2.1
Mailbox Disabled
🔴 552 5.2.2
Mailbox Over Quota
🔴 552 5.2.3
Message Too Large for Mailbox
🔴 552 5.3.4
Message Too Big for System
🔴 550 5.4.1
Recipient Address Rejected
🔴 550 5.4.4
No Route to Destination
🔴 550 5.7.1
Message Rejected by Policy
🔴 535 5.7.8
Authentication Credentials Invalid
🔴 550 5.7.13
User Account Disabled
🔴 550 5.7.14
Trust Relationship Required
🔴 550 5.7.23
SPF Validation Failed
🔴 550 5.7.26
DMARC Policy Violation
🟡 450 4.2.1
Rate Limit: Try Again Later
🟡 452 4.2.2
Mailbox Full (Temporary)
🟡 421 4.4.1
No Answer from Host
🟡 421 4.4.2
Bad Connection
🟡 421 4.4.7
Message Expired in Queue
🟡 421 4.7.0
Temporary Policy Rejection
🟡 421 4.7.28
Blocked: High Complaint Rate

Tier 2 — Common

🔴 550 5.1.0
Other Address Status
🔴 550 5.1.2
Bad Destination Domain
🔴 501 5.1.3
Invalid Address Syntax
🔴 551 5.1.6
Mailbox Has Moved
🔴 550 5.2.0
Other Mailbox Status
🔴 550 5.2.4
Mailing List Expansion Problem
🔴 550 5.3.0
Other Mail System Status
🔴 421 5.3.2
System Not Accepting Messages
🔴 554 5.4.6
Routing Loop Detected
🔴 550 5.4.7
Delivery Time Expired
🔴 550 5.7.0
Message Rejected (Policy)
🔴 550 5.7.2
Mailing List Expansion Prohibited
🔴 534 5.7.9
Authentication Mechanism Too Weak
🔴 550 5.7.24
SPF Validation Error (PermError)
🔴 550 5.7.25
Reverse DNS (PTR) Validation Failed
🟡 421 4.3.2
System Not Accepting Mail
🟡 451 4.7.1
Temporary Auth / Policy Hold
🟡 421 4.7.29
Blocked: Local Policy (New Sender)
🟡 421
Service Temporarily Unavailable
🟡 450
Requested Action Not Taken (Temporary)
🟡 451
Local Processing Error (Temporary)
🟡 452
Insufficient Storage (Temporary)
🔴 500
SMTP Syntax Error
🔴 501
Bad Parameter or Argument
🔴 550
Generic Delivery Failure
🔴 554
Transaction Failed

Provider Documentation

Official bounce and NDR documentation from major email providers and security gateways.

Consumer & Business Email
Transactional & Marketing
Security Gateways
Postmaster & Reputation
Also see: RFC 5321 (SMTP) · RFC 3463 (Enhanced Status Codes) · RFC 3464 (Delivery Status Notifications)